Stabilized trigger circuit



jFIG.l 13

y 1952 M. L. wo'o D 2,598,631

STABILIZED TRIGGER CIRCUIT Filed Dec. 27, 1950 PULSE SOURCE 1'12 Mi/h'am os 150 226 E, m Vo/fs I I Smae'ntor MAR/01V L. WOOD e FWWTT attomeg v Patented May 27, 1952 STABILIZED TRIGGER CIRCUIT Marion Loren Wood, Highland, N. Y., assignor to International Business Machines Corporation, New York, N. Y., a corporation of New York Application December 27, 1950, Serial No. 202,830

Claims.

This invention relates in general to a novel trigger circuit arrangement and more specifically to a trigger circuit having a high degree of stabilization and including a two terminal circuit element such as a crystal diode or a thermistor.

A crystal diode may be briefly described as a rectifying element including a minute block of doped semi-conductor, such as germanium or silicon, having a positive and negative resistance characteristic under certain operating conditions, which is plated with metal on one surface and connected with an extremely fine metallic whisker on the parallel surface.

It has been found that a two terminal variable resistance element such as a crystal diode, for example, having a region of negative variational resistance and connected serially with a constant linear resistance element and a source of potential lends itself to functioning as a trigger circuit having two stable states of equilibrium with the variable resistance element operating in the region of positive variational resistance in one state and in the region of negative variational resistance in the other state. But continuous usage of the diode in a' trigger circuit afiects the stability thereof through the drifting or changing of the characteristic of the diode. While the reason for the drifting of the characteristic of the diode is not readily apparent, it is believed that such may be traced to thermal cycling of the crystal itself.

An object of the invention is to provide a highly stabilized crystal diode trigger circuit.

Another object of the invention is to provide a crystal diode trigger circuit arrangement having means for compensating for the inherent changes in the characteristic of the crystal diode.

A further object of the invention is to provide a crystal diode trigger circuit in which the crystal diode controls the grid bias of an associated electron discharge device resulting in the compensating of the drifting of the characteristic of the diode.

A still further object of the invention is to provide a highly stabilized trigger circuit including a two terminal variable resistance element and an electron discharge device having a positive feedback loop.

A still further object of the invention is to provide a trigger circuit having two stable states of equilibrium and including a two terminal variable resistance element and an electron discharge device such that said element controls the electrical characteristic of said device thereby producing a high stabilized trigger circuit.

A still further object of the invention is to provide a trigger circuit including a two terminal variable resistance element and means for stabilizing the operation of said circuit.

Other objects of the invention will be pointed out in the following description andclaims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is a circuit diagram showing a circuit with which the invention may be practised.

Fig. 2 is an electrical characteristic curve for the circuit arrangement of Fig. 1.

Referring now in detail to Fig. 1, there is shown therein a source of operating potential I0 of the magnitude of approximately 225 volts supplying energy to the trigger circuit through the positive conductor I l and the negative conductor I2. The novel trigger'circuit comprises a current limiting resistor I3, a crystal diode I4, and an electron discharge device I5 serially coupled between conductor II and conductor I2. While a crystal diode is shown in Fig. 1, it should be remembered that the invention is not restricted to the use of a crystal diode but that any two terminal variable resistance element having a region of negative variational resistance may be used in place of the diode. A biasing potential It is applied to the control grid of the device or electron tube I5 through the lower tapped portion of the potentiometer I1 and the grid resistor IS. The wiper I9 is so adjusted that the tube I5 shall always be in a conducting state. That is, the tube I5 will'be conducting for each of the stable positions of the trigger. An impedance or positive feedback loop for compensating for the drift of the characteristic of the diode I4 is coupled from the junction of the anode of the tube I5 and the whisker 24 to the control grid of the tube I5 through the upper tapped portion of the potentiometer I1 and the resistor IS. A source of positive and negative pulses 20 is coupled through the capacitor 2| to the control grid of the device I5 for the purpose of shifting the trigger from one stable position to another in a manner which shall be subsequently described.

The crystal diode I4 includes a minute block of doped semi-conductor 22, such as germanium or silicon, which is plated with a metallic base 23 on one surface and connected with' an extremely fine metallic whisker 24 on the parallel surface. In the case of the germanium diode, when the applied voltage of the base 23 with rer from the off position spect to the whisker 24 is positive, as is the case of Fig. 1, the diode exhibits relatively high resistance properties commonly termed high back resistance. Also when the applied voltage of the whisker 24 with respect to the base 23 is positive the diode exhibits relatively low resistance properties commonly referred to as low forward resist- 7 ance. Thus the crystal diode [4 having the features of a high back resistance and a low forward resistance, which are essential characteristics of a rectifier, functions as a rectifying ele ment. As described in "Crystal Rectifiers by H. C. Torrey and C. A. Whitmer, Radiation Laboratory Series, vol. 15 (McGraw-Hill 1948'), the" rectifying action of the crystal diode resultsfromthe properties of the surface layer of" the semiconductor 22 at the point of contact with the passed by the barrier and the voltage appli'ed'between the whisker and base} were linear, there would be no rectification since the resistance would-be constant. However, this-isnot thecase since this relation is exponential and therefore extremely non-linear thereby making rectification" possible by approximating the characteristic curve of an ideal rectifier. Amore complete description concerning the barrier theory of rectification maybe-found inthe aforementioned textbook.

As" pointed out in the copending application" of Arthur-H. Dickinson, Serial No. 199,687;-filed December 7, 1950, the functioning of the trigger circuit is dependent upon the existence of a negative and positive resistance region inthe crystal diode characteristic curve such asshownini the characteristic curve OB-in Fig; 2. The curve 013' represents the. locus of operating conditions of the diode and is obtainable by static voltage and current measurement. Now disregarding the effeet of the plateto grid coupling for the moment and assuming that the grid bias of the tube .15; is maintained constant, and that the curve 25 (Fig. 2) represents the-characteristic curve for the tube operating at a constant grid-bias, it maybe (Yb?- servedfrom Fig. 2 that the trigger circuit; will have two stable states 26 and 21. Whenzthe trigger is in an off position, it will assume. the1position 26, while when it is in an on'position1 it will assume position 21. The trigger will shift to an on'position' when a positive pulse is applied from the source 2-0" to the control grid. of the tube 15. The trigger will shift from the on positiomto the 01f position when a negative pulsefrom. the source 2! is applied to the control grid? of the tube: 1-5.

However, as alluded to. previously, the characteristic curve OB of. the-diode l4 tends 'to drift due to a thermal and an aging effect. Thuswhen the characteristic curve drifts to theposition 00, thecircuit would be unable to function as a trigger circuit inasmuch as only'one stable state of equilibrium would exist, namely position 28. Like- 'wisev if the characteristic curve should drifttothe position represented by curve OD, the position When anegative potential is apv would represent the only stable condition thereby preventing the circuit from operating as a tri ger circuit.

Now considering the full effect of the anode to grid positive feedback loop or compensating circuit of the tube [5, the characteristic curve AE represents the locus of operating points of the tube: l5 with: the plate togrid feedback loop, which inspection of Fig. 2will show has a sloping central portion appreciably greater than the slope of the characteristic curve 25. Thus the insertion of the compensating or stabilizing feedback'loop in the circuit of Fig. 1 will enable the circuit to assume an equilibrium position at either of two" stable states for the characteristics OB, 0C, and OD. When the characteristic curve for the diode is OB, the two stable positions will be 30 and 3|, while for curve 00 the stable positions will be 32 and 33, and for curve OD the stable positions will be 34 and 35;

In the operation of the-circuit. of Fig. 1-, assuming' that the characteristic curve' OB is the characteristic for the diode- M', the circuit of Fig- 1 willshif-t from the off stable position 30' to the on position 3| when a positive-pulseis applied t'c the control grid of the tube Hi.- T-he'ap'plication ofthe positive pulse tothe control. grid will causethe tube to be made-more conductive thereby causing an increase incurrent fiow therethrough. Ordinarily invacuumtube circuits employing a constant linear resistance element as a plate load, an increase in current flow through the tube will cause the plate-to cathode potential to decrease. Thisis not-the case i'n the circuit of Fig. 1. When the current flow through thetube i5 increases the plate potential increases inasmuch as-the crystal diode passes from-a positive to a negative resistance r'eg ion of'lesser'resistance when the circuitpasses froman off to an onp'osition. The incr'ease in plate potenti'al will, through the compensating loop comprising the upper tapped portion of the potentiometer II and the resistor I8, cause the grid potentialto be-increased. The resulting increase in-grid potential will, in turn, cause an: increase: cur rent flow. This efiect isaccumulative until the onposition3l' is assumed- The-on "position I will be assumed when the diode current equals the tube current and the rate ofchange-ofcurr'ent through the diode with respect to the voltage across the diode is greater in magnitude than the rate of change of current-through the tube: with respect to voltage across thetube'.

The circuit will be shifted from the on positicn- 3i to'the off position 3ii when' a negative pulse is applied to the control grid of the tube from the source 29-; The" negative pulse will render the tube less conductive causing the-plate potential to decrease inasmuch'as the: diode is i caused to pass from a negative to a positive resistance region of. greater resistance. The deicrease in plate potential; will, in'.t'urn,.throug-h the stabilizing loop drive the grid more: negative thereby rendering the tube less conductive. This effectis accumulative until the off position is assumed;

Thus it is to be observed that the resistance of the crystal diode l4 controls the: grid bias-of the tube [5 and that the grid bias cit-the: tube 5.5 will be different for the: twostablestates' of equilibrium. If thecharacteristic curve 013 drifts to-position Oil-for example, the resistance of the. diode at any given-value of current: through the diode will decrease, causing thegrid bias: of the tube l5 to be: less. negative than inthe case when the diode follows the curve B thereby compensating for the drift of the characteristic curve. The dependency of the grid bias of the tube I upon the resistance characteristic of the diode will allow larger drifts in the crystal diode resistance characteristic to be tolerated than vigould be tolerable if the grid bias were held con" s ant.

The following values are relative and are given as one set of values which result in proper opera tion of the crystal diode and the electron tube. This data is not to be construed as the only values that can be used inasmuch as such is dependent upon the characteristics of the diode and the electron discharge device.

Source of Power 10 v01ts 225 Source of Power 16 do 135 Crystal Diode 1N34A Resistor 13 ohms 1200 Electron Tube 15 6SN7 Resistor 17 megohm 0.5 Resistor 18 do 0.1

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodi" ment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A trigger circuit comprising a two terminal' variable impedance element with a characteristic having a positive and negative variational resistance region and operable to two sustained conditions of equilibrium, a biased electron discharge device serially coupled to said element, means including a source of pulses coupled to said device for operating upon said characteristic to produce switching from one condition of equilibrium to the other, and means controlled by said element for determining the bias of said device such that a variation in said characteristic affects the bias of said device thereby compensating fora drift in said characteristic and producing a highly stabilized trigger circuit.

2. A trigger circuit comprising a two terminal variable impedance element with a characteristic having a positive and negative variational resistance region and operable to two sustained conditions of equilibrium, an electron discharge device coupled to said element, biasing means for said device, means coupled to said device for operating upon said characteristic to produce switching from one of said conditions to the other, said element further controlling the bias of said device such that a drifting of said characteristic is compensated for by a corresponding change in the bias of said device.

3. A trigger circuit capable of being transferred from one state of equilibrium to another comprising a crystal diode with a characteristic having a region of positive and negative variational resistance regions, an electron discharge device having a cathode, an anode and a control grid, means coupling said anode to said diode, means biasing said device such that said device is conducting at each of said states, means including a, source of pulses for operating upon said characteristic whereby said diode shifts from one state to another, and impedance means coupling said anode with said control grid for further controlling the bias of said grid, said bias being effective by a drift in said diode characteristic through said anode to grid coupling thereby providing compensation for said drift.

4. A trigger circuit having two stable positions of equilibrium comprising a two terminal variable impedance including a semi-conductor element, an electron discharge device serially coupled to said impedance, said impedance having a characteristic including positive and negative variational resistance regions, said impedance being in a positive resistance region in one of said positions and in a negative resistance region in the other of said positions, means including a source of pulses coupled to said device for inducing a change in said characteristic whereby said circuit shifts from one position to the other, and means operably associated with said device and controlled by said impedance for compensating for a drifting in the characteristic of said impedance.

5. A trigger circuit having two states of equilibrium comprising a two terminal variable resistance element with a characteristic having a positive and negative variational resistance region, an electron discharge device having at least a single control grid, positive feedback means for controlling the electrical characteristic of said device, said feedback means being controlled by said element, said characteristic of said device being difierent in said two states of equilibrium, and means for initiating a change in said characteristics.

MARION LOREN WOOD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,101,525 Bartels Dec. 17, 1937 2,269,001 Blumlein Jan. 6, 1942 2,512,750 Potter June 27, 1950 2,565,497 Harling Aug. 28, 1951 

